Cationic metal carbonyls synthesis

Figure 2. Synthesis of starting metal carbonyl cations...

Metal Atom Synthesis of Organometallic Compounds, IS, 53 Metal Carbonyl Cations, 8, 117... 

B. von Ahsen, M. Berkei, G. Henkel, H. Willner, and F. Aubke, The Synthesis, Vibrational Spectra, and Molecular Structure of [Ir(CO)6][SbF6]3-4HF - The First Structurally Characterized Salt with a Tripositive, Homoleptic Metal Carbonyl Cation and the First Example of a Tetrahedral Hydrogen-Bonded (HF)4 Cluster, J. Am. Chem. Soc. 124, 8371-8379 (2002). 

Aubke has rationalised this approach by postulating that under superacidic conditions highly reactive, extremely electrophilic naked or very weakly solvated cations of low charge are formed (as shown in Sec. 11.3.4.2) and that they function as strong Lewis acids towards CO to form metal carbonyl cations in solution. Aubke and Wang [45] reviewed synthesis and spectroscopic characterisation of several of the compounds described briefly below. 

In a recent comprehensive review Willner and Aubke [48] have set the range of syntheses of transition metal carbonyl cations in superacidic media within the general context of synthesis of these types of cations by all known methods. They have presented the available spectroscopic and crystallographic evidence for the structures of the cations and have discussed the nature of bonding in the carbonyl complexes. 

The properties of the PPN cation have also facilitated the crystallization of salts of the dinuclear metal carbonyl anions, [M2(CO)10]2 (M = Cr, Mo, W), and permitted a crystal-structure determination7 of these remarkable complexes. The dinuclear chromium decacarbonyl anion was first prepared by Behrens and Vogl8 by the reaction of Cr(CO)6 with NaBH4 in liquid NH3 at 40°. More recently Hayter9 prepared dinuclear decacarbonyl anions of all three Group VI metals by a photochemical process and isolated them as the tetraethylammonium salts. A convenient synthesis involving isolation of the PPN salts of these anions is described in Sec. D. 

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